The IRS claims that $30 billion is lost each year in unpaid taxes due to overstated adjustments, deductions, exemptions and credits. To make sure taxpayers don't claim more of a deduction than what is legitimate, the IRS requires certain documentation to use mileage as a business deduction. Taxpayers can claim either the standard mileage rate or actual expenses.

Car and Truck Expenses vs. Commuting Expenses

Car and truck expenses are generally deductible for several reasons. These include travel from one work location to another within the taxpayer's home area; to visit customers; to attend a business meeting at a location other than the regular workplace; or to go to a temporary workplace when the taxpayer has one or more regular work locations. Expenses are not deductible for commuting between a taxpayer's home and regular place of work.

Standard Mileage Rate vs. Actual Expenses

Taxpayers can use the standard mileage rate established by the IRS to claim car and truck expenses. The mileage rate for travel between July 1 and December 31, 2011 is 55.5 cents per mile. Alternatively, they can claim actual expenses incurred for a variety of car-related costs. When the car is used for both personal and business use, expenses must be apportioned accordingly. Taxpayers are free to run a calculation using both methods and use the one that gives them the largest deduction.

Documentation to Support Standard Mileage Rate Claim

To claim the standard mileage rate, the taxpayer must keep a daily log that shows the miles traveled, destination and the purpose of the trip. Documentation that identifies the vehicle and proves the taxpayer owns the car, or is leasing the vehicle, is also required.

Documentation to Support Actual Expenses Claim

Taxpayers can keep a mileage log of all trips, correctly designating each trip as "business" or "personal" to calculate the overall percentage of miles spent on business travel. Taxpayers must keep receipts or invoices to support vehicle costs, which include lease payments, gas, oil, repairs, registration and parking. Taxpayers can claim a percentage of these costs according to the percentage of car miles dedicated to business use. Depreciation cost is also deductible; to support this, taxpayers must have documentation of the original cost of the vehicle, the cost of any improvements and the date the taxpayer began using the car for business.